Tor authorities don't handle votes with more than 64 known-flags
When we get more than 64 known-flags in a vote, we try to stuff them all in an uint64 anyway, and access them by masking with 1<<flagnum. That's undefined behavior right there.
For now, authorities should refuse to accept any vote with more than 64 flags. (We're not even close to that limit right now.) Later, we can use a bitfield instead or something.
This is only a vote issue. Consensus parsing doesn't have this problem, since we just look for the flags we recognize when we're parsing a consensus.
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